Hydraulic systems for heavy equipment, such as excavators, backhoes, bulldozers, front end loaders, earthmovers, etc., typically include a control valve assembly. The control valve assembly is in fluid communication with and receives a flow of a hydraulic fluid from a pump. The control valve assembly is also in fluid communication with a tank, i.e., a fluid reservoir, and circulates the hydraulic fluid back to the tank. The pump then draws the hydraulic fluid from the tank to circulate to the control valve assembly. The hydraulic valve assembly may include a sub-assembly including a first work port and a second work port, each in fluid communication with an actuator, such as a hydraulic piston or a hydraulic motor. The control valve sub-assembly further includes a first valve configured for controlling a flow of the hydraulic fluid through the first work port, and a second valve configured for controlling a flow of the hydraulic fluid through the second work port. The first valve and the second valve operate to control the flow of the hydraulic fluid to the actuator, to thereby control the movement of the actuator. The control valve assembly typically includes multiple control sub-assemblies for controlling multiple actuators.
The control valve sub-assembly may include a first position sensor configured for sensing a position of the first valve, and a second position sensor configured for sensing a position of the second valve. The first position sensor and the second position sensor provide information feedback to a processor of the sub-assembly, i.e., a sub-assembly computer, on the position of the first and second valves respectively, allowing the processor to adjust the position of the first and second valves to achieve a desired flow based upon the respective positions of the first and second valves, i.e., a position control mode.
The control valve sub-assembly may include a first pressure sensor configured for sensing a fluid pressure of the hydraulic fluid at the first work port, a second pressure sensor for sensing a fluid pressure of the hydraulic fluid at the second work port, a pump pressure sensor configured for sensing a fluid pressure of the hydraulic fluid at the pump, and a tank pressure sensor configured for sensing a fluid pressure of the hydraulic fluid at the tank. The first and second pressure sensors provide information feedback to the sub-assembly processor on the pressure of the hydraulic fluid at the first and second work ports respectively, while the pump pressure sensor and the tank pressure sensor provide information feedback to the sub-assembly processor on the pressure of the hydraulic fluid at the pump and the tank respectively. This information combined with the information on the position of the first and second valves respectively, allows the sub-assembly processor to adjust the position of the first and second valves based upon a flow rate, i.e., a flow control mode. However, failure of one of the position sensors prevents the sub-assembly processor from using the position control mode or the flow control mode to control the first and second valves respectively.